Typical elevator systems include an elevator car, e.g., for moving passengers between different floors of the building and a counterweight moving along guiderails in a vertical elevator shaft above or below ground. The car and the counterweight are connected to each other by hoist cables referred herein as elevator ropes. The hoist cables are wrapped around a grooved sheave located in a machine room at the top or bottom of the elevator shaft. The sheave can be moved by an electrical motor, or the counterweight can be powered by a linear motor. Furthermore, the car receives control signals and power signals through a set of electrical cables which have one side attached to the bottom of the elevator car and the opposite side attached to the elevator shaft usually at the mid distance between the top and the bottom position of the elevator car in the elevator shaft.
The sway of the cables refers to an oscillation of the cables, e.g., electrical cables, in the elevator shaft. The oscillation can be a significant problem in an elevator system. The oscillation can be caused, for example, by wind induced building deflection and/or the vibration of the cables during operation of the elevator system. If the frequency of the vibrations approaches or enters a natural harmonic of the cables, then the oscillations can be greater than the displacements. In such situations, the cables can tangle with other equipment in the elevator shaft or get structurally weaker over time, and the elevator system may be damaged.
Various conventional methods control the sway of the elevator cables. For example, the method described in Japan Patent JP2033078A a passive damping mechanical system is added to the elevator shaft at one side of the elevator cables where they attach to the elevator shaft. The passive mechanical system applies a brake to the cables motion which reduced their motion and thus reduces their vibration. Similarly, in the Japan Patent JP2106586A two passive mechanical systems are added to the elevator cables system to damp out their vibrations. One roller-like mechanical system is mounted at the point of connection between the elevator cables and the elevator shaft with a motion of the rollers along the elevator shaft wall, i.e. perpendicular to the vibration of the elevator cables.
Another similar passive mechanical system is mounted under the elevator car at the point of attachment of the elevator cables and the elevator car. This mechanical system includes a roller-like device forcing the cables to move in the axis of vibrations of the elevator cables. Such a mechanical system allows the two extremities of the elevator cables to move in two perpendicular directions, and the brake applied to the rollers damps out the motion of the elevator cables to reduce its vibrations.
However, the passive damping systems increase the cost of the elevator systems and usually configured in advanced reducing their flexibilities.